Particularly in the case of internal combustion engines and transmissions in the automotive area, special requirements with respect to service life, friction and installation reliability are imposed on the shaft seals used in such environments. Radial shaft gaskets with sealing lips of chemically highly resistance polytetrafluorethylene (PTFE) and a helical conveyor structure, for example for a synthetic oil of an internal combustion engine, are known. In this connection, to reduce friction, the lip cross sections widened by the shaft are reduced into the region of the PTFE grain size and the sliding properties of the PTFE which are good anyway are partially promoted by fillers such as graphite or molybdenum disulfide. The seal configuration optimized for the indicated application requires special care during installation to avoid damage to the PTFE sealing lip material which is relatively inelastic compared to fluoropolymer seals. Furthermore, to detect proper positioning of the shaft seal, the shaft seal after its installation is more and more often subjected to automated pressure and/or vacuum testing on the assembly line of the internal combustion engine or of the transmission. Due to the low elasticity of the PTFE sealing lip, its low specific contact force with the shaft, the structure of the shaft contact surface which is amorphous due to its glass fiber fillers, and its helical oil return structure which is open to the atmosphere, its contact region to the shaft cannot be adequately sealed in a gas-tight manner without additional conditioners. For this reason, during the indicated pressure and/or vacuum testing, the sealing gap must be temporarily sealed, for example by using a wax which is volatile with respect to the operation of the transmission or the internal combustion engine. In such a case, a faulty wax application process or installation-induced damage of the wax layer during the indicated pressure and/or vacuum testing can lead to an apparent leak. This undesirably leads to rejection of the actually serviceable shaft seal and thus of the transmission or internal combustion engine.
The object of this invention is therefore to devise an improved sealing element which has good sealing properties with simple and this economical producibility both in the intended operation and also for test purposes.